Relative genotypic frequency after selection

TLS Online TPP Program

#Id: 3706

#Unit 2. Cellular Organization

When a genome contains a cluster of genes with related sequences, mispairing between nonallelic loci can cause unequal crossing over. This produces a deletion in one recombinant chromosome and a corresponding duplication in the other.

TLS Online TPP Program

#Id: 3707

#Unit 2. Cellular Organization

Thalassemias result from occurrence of unequal crossing that reduce or prevent synthesis of either a- or b-globin

TLS Online TPP Program

#Id: 3708

#Unit 2. Cellular Organization

Different thalassemias are caused by various deletions that eliminate a- or b-globin genes. The severity of the disease depends on the individual deletion.

TLS Online TPP Program

#Id: 3709

#Unit 2. Cellular Organization

Depending on the diploid combination of thalassemic alleles, an affected individual may have any number of a chains from zero to three.

TLS Online TPP Program

#Id: 3710

#Unit 2. Cellular Organization

if an individual has only one a gene, the excess b chains form the unusual tetramer b4, which causes hemoglobin H (HbH) disease. The complete absence of a genes results in hydrops fetalis, which is fatal at or before birth.

TLS Online TPP Program

#Id: 3711

#Unit 2. Cellular Organization

Hb anti-Lepore, Hb Kenya result from unequal crossing over between linked genes